1. Field of the Invention
The present invention relates to a coil apparatus in an inductor, a transformer or the like such as a choke coil which is utilized in a switching power supply and the like.
2. Description of the Related Art
A one-turn coil constituted of a metal plate is used as a choke coil or a low-voltage side coil of a transformer in a switching power supply or the like with a large current capacity in the prior art. For instance, Japanese Unexamined Patent Publication No. 97054-1996 discloses a transformer constituted by utilizing such a metal plate. This transformer assumes a structure achieved by laminating a high-voltage side coil and a low-voltage side coil via an insulating case formed in a plate shape and housing the high-voltage side coil and the low-voltage side coil in a case-like insulating member.
In the coil apparatus in the prior art described above, various members must be provided for insulation, presenting a problem in that the number of required parts is bound to be large.
In addition, the coil apparatus disclosed in the publication mentioned above includes an internal circumferential coil terminal 51 of a flat-face coil 50 that is spirally wound provided on the flat-face coil 50, as shown in a sectional view presented in FIG. 8A. Reference numeral 52 indicates an external circumferential coil terminal of the flat-face coil 50.
The coil structure disclosed in the publication having the internal circumferential coil terminal 51 placed on the flat-face coil 50 has a large height h1, resulting in a poor space factor. This problem becomes even more pronounced if flat-face coils 50 are laminated as shown in FIG. 8B in a transformer with a large turn ratio, since the thickness h2 increases. In addition, the problem worsens in a transformer with a large power capacity constituted by using a thick wiring material.
The insulating case in the coil apparatus disclosed in the publication if adopts a double cylinder structure having one side along the axial direction left open with notches for leading out the coil terminals provided at two positions facing opposite each other at the outer cylinder. The high-voltage side coil, the low-voltage side coil and an insulating spacer are housed inside the insulating case. The main magnetic legs of the split cores are inserted at the inner cylinder of the insulating case, and the side magnetic legs are provided outside the outer cylinder of the insulating case. The bridging portion between the main magnetic legs and the side magnetic legs of one of the split cores is set facing opposite the high-voltage side coil via the insulating spacer in this structure.
In the coil apparatus in the prior art described above in which the low-voltage side coil and the high-voltage side coil are set facing opposite each other via the insulating spacer and the coil terminals and the core, too, are set facing opposite each other via the insulating spacer, the distance which only corresponds to the thickness of the insulating spacer can be assured for the insulating distance between the high-voltage side coil and the low-voltage side coil and as the insulating distance between the high-voltage side coil and the core. For this reason, the coil apparatus cannot be utilized in a transformer that requires a larger insulating distance between the high-voltage side coil and the low-voltage side coil or between the high-voltage side coil and the core for safety reasons or due to characteristics-related requirements.
Japanese Unexamined Patent Publication No. 335158/1993 discloses other examples of a coil and a transformer constituted by using a metal plate. The coil and the transformer adopt a structure achieved by preparing coils assuming various coil terminal shapes, sequentially connecting the coils via spacers so as to allow the connecting portions where the coils are connected turn around along the direction of the circumferences of the coils and laminating them via insulating sheets.
This coil apparatus in the prior art poses problems in that the number of parts is bound to be large since coils in various shapes are utilized and in that a larger space is required for the connections.
It is an object of the present invention to provide a coil apparatus that makes it possible to insulate a one-turn coil from an adjacent member while utilizing a smaller number of members by addressing the problems of the prior art discussed above.
It is a further object of the present invention to provide a power transformer provided with a spirally-wound coil that achieves a structure with a small height by improving the space factor of the coil.
It is a still further object of the present invention to provide a power transformer in which a sufficiently large insulating distance is assured between the high-voltage side coil and the low-voltage side coil and between the high-voltage side coil and the core.
The coil apparatus according to the present invention comprises a coil, an insulating case and a core. In the coil apparatus according to the present invention, the coil includes at least a one-turn coil constituted of a metal plate, the outer periphery is formed in a ring shape having a pair of coil terminals provided at one end thereof and a projecting retaining piece provided at another end thereof. The insulating case includes a plate member having a magnetic leg insertion hole at which main magnetic legs of the core is inserted, with a fitting wall at which the coil is fitted provided around a coil mounting surface at the plate member, notched portions provided at a coil terminal mounting side and the opposite side from the coil terminal mounting side at the fitting wall of the insulating case, a first retaining portion and a second retaining portion for retaining the coil provided at extended portions extending along the radial direction at the notched portions, the coil fitted in at the fitting wall and the coil terminal and the retaining piece of the coil respectively retained at the first retaining portion and the second retaining portion to prevent the coil from lifting off the insulating case. The core is constituted of split cores each having main magnetic legs, side magnetic legs and a bridging portion between the main magnetic legs and the side magnetic legs, with the main magnetic legs of the core inserted at the coil, the side magnetic legs set toward the external circumference of the insulating case and one bridging portion set facing opposite the coil over a distance.
In this structure, the 1-term coil constituted of a metal plate which is housed inside the insulating case is insulated on one side from other members that are adjacent to it such as the core, a coil and the like by the plate member of the insulating case. A sufficient gap is formed between the coil and another member, which may the core on the opposite side with the front end of the fitting wall of the insulating case coming in contact with the other member such as the core and insulation is achieved by the gap. As a result, the coil apparatus can be achieved without having to utilize an insulating sheet, i.e., with a smaller number of parts.
In addition, the coil apparatus according to the present invention assumes a structure in which the retaining piece at the coil is retained at the second retaining portion of the insulating case with a sufficient retaining margin to allow it to move along the rotational direction relative to the second retaining portion and the first retaining portion of the insulating case is used to retain at least either of the pair of coil terminals as the coil is turned.
In a structure which allows a coil terminal to be retained by rotating the coil as described above, the coil can be connected and retained at the insulating case through a simple process.
In addition, the coil apparatus according to the present invention may further comprise a bobbin and another coil wound around the bobbin. The bobbin includes a cylindrical winding drum and flanges formed at the two ends of the winding drum. The insulating case includes a side wall projecting out from an outer side of the plate member to the opposite side from the fitting wall to house the bobbin having the other coil wound around it inside the side wall, with the coil terminal of the other coil led out through a notched portion provided at the side wall of the insulating case.
In this structure, the one-turn coil and the other coil are insulated from each other by the plate member, the fitting wall and the side wall of the insulating case, achieving reliable insulation without requiring a special insulating member. In addition, the insulation between the other coil and the core, too, is assured without a special insulating member, since the bobbin having the other coil wound around it is enclosed by the side wall of the insulating case.
Alternatively, the coil apparatus according to the present invention may include at least two one-turn flat coils each constituted of a metal plate. The coils are each provided with a pair of coil terminals projecting outward from a main body, with one of the coil terminals in the pair formed so as to allow a line passing through the center of the coil terminal along the widthwise direction to pass the center of the coil. The two coils formed identically to each other are placed one on top of the other by setting one of the coils in reverse orientation, aligning its axis to the axis of the other coil and electrically insulating the one coil from the other to electrically connect the one coil terminal in the one coil to the one coil terminal in the other coil.
Since a two-turn coil is constituted by connecting identical coils with one of them reversed, it is not necessary to provide different types of coils, thereby achieving a reduction in the number of required parts and a reduction in the space required for connection.
In the coil apparatus according to the present invention described above, the main body of each coil assumes a toroidal shape.
By forming the coils in a toroidal shape as explained above, a coil apparatus which facilitates the assembly process of fitting the core with the section of the main magnetic leg formed in a cylindrical shape at the center of the coil is achieved.
The main bodies of the coils in the coil apparatus according to the present invention may also be formed in a toroidal shape with angular corners.
By forming the coils in a toroidal shape with angular corners in this manner, a coil apparatus which facilitates the assembly process when fitting cores with a section of the main magnetic legs formed in a polygonal shape at the center of the coil is achieved.
Furthermore, in the coil apparatus according to the present invention, the one-coil terminal in each coil includes a staged portion with a connecting portion to be connected with another coil provided at a flat surface different from the coil main body at the front end of the staged portion so that the two coils are coupled with another coil present between the coil main bodies.
In addition, according to the present invention, the different coil in the coil apparatus is a winding wound around a bobbin.
With a different coil provided in the space created between the coil main bodies by forming staged portions at the coil terminals, it becomes possible to constitute a coil apparatus having a plurality of windings such as a transformer.
In the coil apparatus according to the present invention, the other coil terminal in each of the coils includes a staged portion ranging over xc2xd of the thickness of the coil with a connecting portion to connect with another member provided at a flat surface different from the coil main body at the front end thereof, and the two coils are coupled with each other with the other coil terminals thereof set flush with each other.
This structure in which the other coil terminals constituting connecting terminals to be connected with other members are set flush with each other, the positions of the two coil terminals can be adjusted to the height of the connectors of the other members when, for instance, the coil apparatus is mounted on a substrate.
As a further alternative, the coil apparatus according to the present invention may comprise a bobbin, a high-voltage side coil, a low-voltage side coil and a core and constitute a power transformer. The bobbin includes a cylindrical winding drum and flanges formed at the two ends of the winding drum. The high-voltage side coil assumes a structure achieved by laminating in the axial direction flat-face coils spirally wound around the winding drum over two layers so as to allow the two-layer flat-face coils to sit continuous to each other on the internal circumferential side. The low-voltage side coil is constituted of a metal plate formed in a roughly U-shape and is set further outward relative to a flange. The core is constituted of split cores each having main magnetic legs, side magnetic legs and a bridging portion bridging between the main magnetic legs and the side magnetic legs, with the main magnetic legs of the core inserted at the winding drum, the side magnetic legs set on the external circumferential side of the flanges and the bridging portions and the side magnetic legs set so as to enclose at least parts of the high-voltage side coil and the low-voltage side coil.
This structure allows the coil terminals to be led out from the external circumference of the flat-face coils achieving a two-layer structure and thus, since the coil terminals are not placed the flat-face coils, the space factor is improved and the height does not increase. In addition, since the low voltage side coil is constituted as a one-turn coil by using a U-shaped metal plate, the low-voltage side coil has a low profile, and when this low-voltage side coil is coupled with the high-voltage side coil, a thin power transformer is realized.
In addition, in the coil apparatus according to the present invention, the winding drum includes a winding isolation piece projecting further outward relative to the external circumference of the cylindrical portion, and the flat-face coils are overlaid via the winding isolation piece.
By further providing the coil apparatus with a winding isolation piece at the winding drum of the bobbin and overlaying the flat-face coils via the winding isolation piece in this manner, any irregularities in the turns at the windings are prevented.
Furthermore, in the coil apparatus according to the present invention, low-voltage side coils may be set further outward relative to the flanges formed at the two ends of the winding drum.
By providing the low-voltage side coils on the outside of the two flanges at the bobbin around which the high-voltage side coil is wound as described above, the high-voltage side coil and the low-voltage side coils can be coupled with a higher degree of reliability to achieve a transformer with superior characteristics. In addition, since the low-voltage side coils are provided on the two sides of the bobbin, more options are afforded with regard to the connections of the low-voltage side coils to allow the coil apparatus according to the present invention to be adopted in conjunction with various types of converter transformers.
The coil apparatus according to the present invention may further comprise an insulating case that includes a first case and a second case each provided with a plate member having a magnetic leg insertion hole at which main magnetic legs of the core is inserted and a side wall formed almost perpendicular from an outer side of the plate member. The side walls of the first case and the second case overlap each other along the radial direction of the coils and each have a notched portion for a winding lead out. A terminal of the high-voltage side coil is led out through the notched portion with the insulating case covering the bobbin around which the high-voltage side coil is wound, the low-voltage side coil formed in a roughly U-shape is set on the outside of the plate member of at least either the first case or the second case of the insulating case, the main magnetic legs of the core inserted at the winding drum, the low-voltage side coil and the magnetic legs insertion holes of the insulating case and the side magnetic legs of the core are set on the outside of the side walls of the insulating case.
This structure further increases the creepage distance between the core and the low-voltage side coils and the creepage distance between the core and the high-voltage side coil to insulate them from each other with a higher degree of reliability.
Alternatively in the coil apparatus according to the present invention, the external circumference of each of the low-voltage side coils may be formed in a round shape, with a pair of coil terminals projecting out at one end of the external circumference and a retaining piece projecting out at another end. The coil apparatus further includes an insulating case that covers the bobbin, with the insulating case having a magnetic leg insertion hole provided at each of plate members to be set over the flanges of the bobbin. An outer surface of the insulating case located on the opposite side from the bobbin constitutes a low-voltage side coil mounting surface and a fitting wall at which the low-voltage side coil is fitted is provided around the mounting surface. Notched portions are formed at the fitting wall on the side where the coil terminals of the low-voltage side coils are mounted and also on the opposite side, and a first retaining portion and a second retaining portion for retaining the low-voltage side coil are provided at extended portions extending along the radial direction at the notched portions so that the low-voltage side coil is fitted at the fitting wall and the coil terminal of the low-voltage side coil and the retaining piece are retained at the first retaining portion and the second retaining portion to prevent the low-voltage side coil from lifting off the insulating case.
With the low-voltage side coil secured to the insulating case by adopting a structure through which the low-voltage side coil is prevented from becoming lifted by the retaining portions, a sufficient distance is assured between the low-voltage side coil and the core to achieve reliable insulation with ease without having to utilize a special member.
As a further alternative, the coil apparatus according to the present invention may comprise a bobbin, an insulating case, a high-voltage side coil, a low-voltage side coil and a core and may constitute a power transformer. The bobbin includes a cylindrical winding drum and flanges formed at the two ends of the winding drum. The high-voltage side coil, which is wound around the winding drum is housed together with the bobbin inside the insulating case. The insulating case includes a first case and a second case each provided with a plates member having a magnetic leg insertion hole at which main magnetic legs of the core is inserted and a side wall formed almost perpendicular from an outer side of the plate member. The side walls of the first case and the second case overlap each other along the radial direction of the coil and each have a notched portion for winding lead out. A terminal of the high-voltage side coil is led out through the notched portion with the insulating case covering the bobbin around which the high-voltage side coil is wound, and the low-voltage side coil which is constituted of a metal plate formed in a roughly U-shape is set on the outside of the plate member of at least either the first case or the second case. The core is constituted of split cores each having a main magnetic leg, the side magnetic legs and a bridging portion bridging between the main magnetic legs and the side magnetic legs, with the main magnetic legs of the core inserted at the winding drum, the low-voltage side coil and the magnetic leg insertion hole of the insulating case and the side magnetic legs of the core set further outward relative to the side wall of the insulating case.
This structure further increases the creepage distance between the core and the high-voltage side coil and the creepage distance between the low-voltage side coils and the high-voltage side coil, to insulate them from each other with a higher degree of reliability.
In addition, in the coil apparatus according to the present invention described above, low-voltage side coils may be provided outside the plate members of the first case and the second case.
By providing the low-voltage side coils on the outside of the two flanges of the bobbin around which the high-voltage side coil is wound as described above, the high-voltage side coil and the low-voltage side coils can be coupled with a higher degree of reliability to achieve a transformer with superior characteristics. In addition, since the low-voltage side coils are provided on the two sides of the bobbin, more options are afforded with regard to connections of the low-voltage side coils to allow the coil apparatus according to the present invention to be adopted in conjunction with various types of converter transformers.
Furthermore, in the coil apparatus according to the present invention, the external circumference of each of the low-voltage side coils is formed in a round shape with a pair of coil terminals projecting at one end of the external circumference and a retaining piece projecting out at the other end. The insulating case includes a fitting wall at which the low-voltage side coil is fitted is provided around a low-voltage side coil mounting surface, and notched portions are formed on a coil terminal mounting side on where a coil terminal of the low-voltage side coil is mounted and on the opposite side at the fitting wall of the insulating case, with a first retaining portion and a second retaining portion for retaining the low-voltage side coils provided at extended portions extending along the radial direction at the notched portions. The low-voltage side coil is fitted at the fitting wall and the coil terminals and the retaining piece of the low-voltage side coil are retained at the first retaining portion and the second retaining portion to prevent the low-voltage side coil from lifting off the insulating case.
With the low-voltage side coil secured to the insulating case by adopting a structure through which the low-voltage side coil is prevented from becoming lifted by the retaining portions, a sufficient distance is assured between the low-voltage side coil and the core to achieve reliable insulation without having to utilize a special member.